The present invention concerns a process for the bleaching of cellulosic or cellulosic/synthetic fibers and fabrics by means of oxidizing agents such as hydrogen peroxide, persalts and sodium peroxide in the presence of particles of iron or of ferrous metals and a stability composition therefor.
The presence of metallic particles on fabrics during the course of bleaching is due to numerous factors: remains of hoop-irons rusted onto the bales of cotton, sharpening of carding brushes during spinning, use of iron vats for the preparation of sizing, abrasion of combs during the course of weaving, rust of pipes transported by the water used for washings and bleaching baths and the like.
The mechanism of fiber degradation in the presence of particles of iron or of ferrous metals during the course of bleaching by oxidation is well known and long been a concern.
The metallic particles catalyze the decomposition of the oxidizing agent used for bleaching, causing an alteration of the fibers by the formation of oxycellulose. These alterations are localized at the sites where the catalyst adheres to the fiber. They manifest themselves by the formation of holes having the form of points or of streaks, while the remainder of the fabric can be absolutely faultless.
Also, when the alteration is less pronounced, there is the formation of spots during dyeing, with the coloring agent having a different affinity for the cellulose and the oxycellulose. These phenomena have been abundantly described in the literature; notably in:
Technologie Chimico-textile. Blanchimentteinture. Impression en Apprets 1st volume by Gustave CAPRON. PA0 Textile Chemistry--Impurities in fibers. Purification of fibers by R. H. PETERS--Vol. II, p. 11 (1969). PA0 The principles of bleaching and finishing of cotton--3rd edition by S. R. TROTMAN M.A. Fic. p. 510 (1927). PA0 Acitvators and stabilizers for peroxide bleaching. (in German). Text. Prax. Int. 29 (1974) by Dr. P. NEY p. 1552-1565. PA0 (a) Random distribution of metallic particles in the unbleached fabrics (this distribution was brought about by means of an acid solution of sodium thiocyanate). The phenomenon was standardized for all the examples by introducing a rusty pin into each sample of unbleached fabric; PA0 (b) Impregnation of the unbleached fabric in the blecing bath or desizing/bleaching bath and then squeezing the fabric in order to leave in the fabric only the quantity of bath required for the reaction (this quantity has been fixed at 100% by weight of dry fabric); PA0 (c) steaming the fabric in order to raise the temperature thereof to the desired temperature of about 30.degree.-35.degree. C. PA0 (d) Deposition by rolling up the fabric or placing it into folds for 30 minutes at the noted temperature; and PA0 (e) Washing of the fabric at 90.degree.-95.degree. C.; then at 60.degree. C.; and lastly in cold water.
The degradations occasioned by the presence of particles of iron or of ferrous metals during the course of bleaching textile fabrics thus translate into an irreversible degradation of the fibers and because of this fact lead to important losses for the bleaching enterprises.
Since, as has been shown further above, the origins of these particles are numerous, the problems posed by the latter are of a serious nature.
Consequently, there exists an industrial need responding to a constant worry of the profession of textile embellishing, to have a suitable process at their disposal.
A solution utilized in the prior art consisted of carrying out a an alkaline treatment of the fabric in the hot state. This operation which is situated between sizing removal and bleaching cannot be carried out in the case of a simultaneous desizing/bleaching operation. Furthermore, this treatment consumes energy and its effectiveness can be limited since the water which is used in the later rinsing operation can contain traces of iron in the form of rust.